Tesco is facing Britain's largest ever equal pay claim and a possible compensation bill of up to 4 billion pounds (C$7 billion), according to a law firm which has begun legal proceedings. It comes as a campaign for equal pay grows in the U.K.

The workers were suspected of being union sympathizers, the board reported, and Mexico altered documents in an attempt to cover up its union-busting activities.

United Food and Commercial Workers Canada (UFCW) Local 1518 presented evidence of the blacklisting to the BCLRB in 2012. The union represents migrant workers at Sidhu & Sons Nursery Limited in the B.C. Lower Mainland.

The labour board’s March 20 ruling came after years of legal wrangling, the union said, with Mexico attempting to stall — and ultimately quash — charges.

“It has been a long battle, but finally the truth has won out,” said Ivan Limpright, president of UFCW Canada Local 1518. “Every worker in Canada has the right to join a union, including migrant workers. Mexico’s blacklisting and coercion violated Canadian laws and the rights of workers involved.”

“Will the premier, given the decision and the ruling of B.C. Labour Relations Board, take action to ensure that workers in that situation get the same rights as every other worker in British Columbia?” asked NDP leader of the opposition Adrian Dix. “Will she take action? Will she join with me, for example, in sending a joint letter to the Mexican consulate saying that this practice is completely unacceptable to her?”

While Clarke declined to comment on the co-signing of a letter, she said the province has every intention of fulfilling its responsibilities to workers.

“Every worker in British Columbia has the right to be protected,” Clarke said. “Every worker in British Columbia deserves to know that the law is there to protect them. We believe in that. We stand for that, and those rules exist across the board to protect people no matter where they come from. “